Learning objective

• At the end of this lesson student should be able to:

–Measure physical quantities using appropriate instrument

– Explain accuracy and consistency

– Explain sensitivity

Differentiate the distribution of gunshot below

Figure (a) Figure (b)

ExplanationFigure (a)• Shots are closer to the target but scattered

from each other.• In other word, we can say all shot are

accurateFigure(b)• All shots are close to each other but far from

the target• In other word, we can say that all shots are

consistent

What exactly means of consistency and accuracy???

Introduction• Every measurement of a physical

quantity is an estimation only.

• No measurement is exactly accurate and consistent

• For example, 500 g of rice bought from a retail shop maybe 500.1 g or 499.9 g

Consistency• If all the reading are the same or if the

variations are small, then the measurements are consistent

• Consistency of the measuring instrument is the ability of the instrument to produce reading that are consistent with little or no variations.

• Precise electronic measuring instruments such as the electronic balance usually produce consistent reading.

Electronics balances

Accuracy • The accuracy of measuring instrument is the

ability of the instrument to give measurements of a physical quantity which are close to the actual value.

• How to increase accuracy during take a reading? To increase accuracy during take a reading is take a reading many time (at least 3 times)

According to the picture beside, interpret the distribution of gun shots.

• From the picture above we can say that the distribution of gun shots is accurate and consistent.

• This because all gun shots closest each other and closest to the target.

Which of the following picture show us not accuracy but consistent?

BA

C D

Which of the following picture show usaccuracy and consistent?

A B

C D

Which of the following picture show us accuracy but not consistent?

A B

C D

Example :• The actual height of the table is 56.2cm.

Two students, Ahmad and Bakri measure the height of the table and obtain the following data:

Ahmad (x)

56.3cm 56.2cm 56.1cm 56.4cm

Bakri(.)

57.0cm 57.0cm 57.1cm 57.1cm

Solution

For Ahmad,

• His reading are considered accurate because they are very close to the actual reading

• His reading are considered not consistent because there are variations between the readings

For Bakri,

• His reading are considered inaccurate because they are far from the actual reading

• His readings are considered more consistent because they are concentrated on two values only

1. If a group of students from your class leave for Japan by plane, how are the readings on their watches when they arrive in Japan?

A. Accurate but not consistentB. Consistent but not accurateC. Not consistent and not accurateD. Accurate and consistent

Answer: B

Quiz

Screw clamp to ensure that reading does not change while the scale is being read

Part of Vernier Callipers with their functions

Method of Reading Vernier Calipers

1. Determine the reading on the main scale, which is the value on the main scale just before the zero mark on the Vernier scale

The reading on main scale = 2.3cm

2. Determine the reading on the Vernier scale, which is the marking on the Vernier scale which coincides with a marking on the main scale.

Vernier scale reading = 0.4 mm= 0.04 cm

3. The total reading is obtained by adding the reading on the main scale with the reading on the Vernier scale.

Will a measurement taken using this Verniercalipers be accurate? Why?

• No, because this Vernier calipers has zero error. The ‘0’ mark on the main scale is not in line with the ‘0’ mark on the vernier scale when jaws of the vernier calipers is closed

Zero Error on the Vernier Calipers

• There are two type of zero error on the Verniercalipers :

– Positive Zero Error

– Negative Zero Error

Positive zero error

Negative zero error In case you get the negative zero error, the value you obtain from Verniercaliper must be subtract with 0.1

Micrometer screw Gauge

How reading Micrometer Screw Gauge

Main scale ade dua scale:• Atas : yg mane setiap scale ni bermula dgn

0,1,2………• Bawah: yg bwh pula setiap satu bernilai 0.5

0.5

1

• Semasa mengambil bacaan di ‘main scale’ pastikan scale ygkat bawah tu nampak atau tidak. Klau nampak, nilai yg katbawah kena tmbh dgn nilai yg kat atas.

• So, skrg bacaan di ‘main scale’ ialah 1.5

• Then take a reading on thimble scale. Bacaan yg kitaambil adalah line on thimble scale yang coinside dgngaris tengah on the main scale.

• Berdsarkn gmbr diatas, 37 adalah garis yg coinsides…• Then, 37 X 0.01 = 0.37 , ini kerana setiap scale line

bernilai O.O1 mm

• Reading on main scale + Reading on thimble scale

• 1.5 + 0.37 = 1.87 mm

Positive zero error

If ‘0’ mark on main scale is locate above than ‘0’ mark on thimble scale, you will get positive zero error

Negative zero errorIf ‘0’ mark on main scale is locate below than ‘0’ mark on thimble scale, you will get negative zero error

1. Students measure the same book. But why they get different reading?• Because use the different type of instruments.

2. Which instruments is sensitive? Why?• Micrometer screw gauge because can read up

to 3 decimal place.

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